This invention relates to a navigation system for use in a vehicle which displays a route guide for guiding the vehicle along an optimum route.
A general navigation system for use in a vehicle beforehand computes an optimum route from a starting point to a destination prior to the start of the vehicle, and a route guide corresponding to the current position of the vehicle is displayed in its display unit after the start of the vehicle, so that the vehicle may be guided to the destination along the optimum route.
In the navigation systems disclosed in Japanese Laid-Open Patent Application No. 150700/91 and Japanese Patent Publication No. 36038/90, respectively, a direction indicating image indicating the direction of vehicle travel at the intersection, where the vehicle should turn, and the name of the road the vehicle is to enter at that intersection are displayed on the display unit. In the above-mentioned systems, in order to enable the driver to correctly recognize the intersection where the vehicle should turn, a bar graph representing the distance from the current position of the vehicle to the intersection where the vehicle should turn next is displayed on the display unit. Seeing this bar graph, the driver may recognize the distance to the intersection where the vehicle should turn next. This makes it possible for the driver to prepare for the next turn. However, there are instances where the above distance information is not enough for the driver to make a correct decision as to when the vehicle should change its lane in order to make the next turn. After the vehicle changes lanes in accordance with the distance information, it is possible that there are other roads which intersect the road on which the vehicle is currently travelling between the point where the vehicle changes lanes and the intersection where the vehicle is to turn. In that event, the driver has no choice but to turn onto the intersection road. As a result, the driver has strayed from the optimum route. If the driver does not change lanes until he is very near the intersection where the vehicle is to turn to avoid the possibility of other roads intersecting the road on which his vehicle is currently travelling, the driver may not be able to change lanes with the result that he vehicle cannot turn at the intersection where the vehicle should turn, particularly when there is heavy traffic. As a result, the driver has strayed from the optimum route. As described above, the above-mentioned distance display means is unable to fully exhibit its function.
In Japanese Laid-Open Patent Application No. 150700/91, marks representing buildings, and other structures located in the vicinity of the intersection where the vehicle is to turn are displayed on the display unit in order to facilitate the driver's easy recognition of the aforesaid intersection. However, since the driver cannot recognize the buildings until the vehicle is very near the intersection where the vehicle is to turn, the above-mentioned disadvantages cannot be eliminated.